Cationic polymerization is initiated by a cation generated from a cationic polymerization initiator and is not inhibited by oxygen. For this reason, cationic polymerization is not subject to such restriction as necessity of performing polymerization in an inert atmosphere and can be carried out advantageously in air rapidly and completely. A cationically polymerizable composition is suitable for use in paints, inks, adhesives, photoresists, molding materials, and the like and these applications demand not only excellent polymerizability but also good storage stability.
The prior-art documents relating to this invention are listed below.
Patent document 1: JP2001-200049 A
Patent document 2: JP2003-292606 A
Patent document 3: JP2001-30281 A
Patent document 4: JP3566397
Patent document 5: JP05-5006 A
Patent document 6: JP06-41215 A
Patent document 7: JP10-310633 A
Patent document 8: JP58-57429 A
Non-patent document 1: Kobunshi (High Polymers, Japan), 45, (3), 128 (1996)
The catalysts known for cationic polymerization include onium salts represented by sulfonium salts described in the patent documents 1, 2, 4, 5, and 6, diazonium salts and iodonium salts described in the patent document 1, and bisallene type metal complexes described in the patent document 3. Of these cationic polymerization catalysts, benzenesulfonium salts are studied most widely as described in the non-patent document 1 and some of them are commercially available as San-aid series from Sanshin Chemical Industry Co., Ltd. Compounds showing the highest activity among the aforementioned sulfonium salts, diazonium salts, and iodonium salts are antimony salts such as SbF6, SbCl6, and SbF5(OH). However, antimony is a highly toxic substance and is not desirable for practical use.
As an example of the means to solve the aforementioned problems, the use of a heteropolyacid as a curing agent for epoxy resins is described in the patent document 8. However, heteropolyacids are ultrastrong acids, show an extremely high curing activity, initiate curing at normal temperature to cause gelation in a short time, and show poor stability as a composition. Hence, heteropolyacids are difficult to use in practice.